Integrated circuit with multi-length power transistor segments

ABSTRACT

A monolithic integrated circuit fabricated on a semiconductor die includes a control circuit and a first output transistor having segments substantially equal to a first length. A second output transistor has segments substantially equal to a second length. The first and second output transistors occupy an L-shaped area of the semiconductor die, the L-shaped area having first and second inner sides that are respectively disposed adjacent first and second sides of the control circuit. At least one of the first and second output transistors is coupled to the control circuit. It is emphasized that this abstract is provided to comply with the rules requiring an abstract that will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. 37 CFR 1.72( b ).

RELATED APPLICATIONS

This is a continuation-in-part (CIP) application of application Ser. No.10/974,176 filed Oct. 26, 2004, entitled, “INTEGRATED CIRCUIT WITHMULTI-LENGTH POWER TRANSISTOR SEGMENTS”, which is assigned to theassignee of the present CIP application.

FIELD OF THE INVENTION

The present invention relates generally to the field of semiconductordevices; more specifically, to monolithic integrated circuits (ICs) andto methods of manufacturing IC devices.

BACKGROUND OF THE INVENTION

Integrated circuits (ICs), including power integrated circuits (PICs),find application in an increasingly wide variety of electronic devices.Typically, PICs comprise one or more high-voltage field effecttransistors (HVFETs) having a device structure such as those disclosedin U.S. Pat. No. 6,207,994 (“the '994 patent”), which is hereinincorporated by reference. Each of the devices disclosed in the '994patent has a source region and a drain region separated by anintermediate region. A gate structure is disposed over a thin oxidelayer over the metal-oxide-semiconductor (MOS) channel of the device. Inthe on state, a voltage is applied to the gate to cause a conductionchannel to form between the source and drain regions, thereby allowingcurrent to flow through the device. In the off state, the voltage on thegate is sufficiently low such that no conduction channel is formed inthe substrate, and thus no current flow occurs. In this condition, highvoltage is supported between the drain and source regions.

Most integrated circuits contain one or more output transistors thatcontrol current flow through one or more external loads. By way ofexample, FIG. 7 of the '994 patent discloses a structure havinginterdigitated source and drain regions that is commonly utilized as anoutput transistor in many types of power devices. In the design of aparticular PIC, these elongated source/drain segments may be replicatedto increase the current handling capability of the power device.

FIG. 1 shows a typical prior art IC fabricated on a semiconductor die 10having an aspect ratio defined as the ratio of the length (L) to thewidth (W). Included on semiconductor die 10 is a control circuit 11 thatis utilized to control on/off switching of an output transistor 12. InIC designs, it is customary to utilize a single standardized controlcircuit design coupled to a variety of output transistor layouts ofdiffering sizes (e.g., number of segments) to create a family of deviceswith similar functionality, but with differing current handlingcapability. For example a family of ICs, each with differing currenthandling capabilities, may be created by increasing the number ofparallel segments of transistor 12. According to this traditionalapproach, ICs with larger current handling capability have a largerwidth (W) to accommodate more source/drain segments, but the same length(L). In other words, in prior art IC designs, the length of the outputtransistor is substantially constant, and equal to the length of controlcircuit 11. Integrated circuit devices with more current handlingcapability have more segments added in parallel, which increases thewidth of the semiconductor die.

To achieve maximum utilization of the package space that housessemiconductor die 10, control circuit 11 is usually designed with alength that is much larger than its width. For example, in a typical ICproduct family the smallest device is designed to be long and narrow(i.e., large aspect ratio), with larger devices having an increasedwidth dimension due to the added number of output transistor segments(i.e., smaller aspect ratio). That is, the aspect ratio of largerdevices decreases as more segments are added.

Aspect ratio is a critical parameter in the design of most monolithicICs, including, by way of example, power integrated circuit devices. AnIC fabricated on a semiconductor die having a very large or very smallaspect ratio often suffers from mechanical stress caused by the moldingcompound used to package the die. This stress can adversely change theelectrical properties of the IC circuitry. For minimum stress asemiconductor die should have an aspect ratio that is close to 1.0,i.e., a length that is substantially equal to its width. The difficulty,however, is that the output transistors are often required to haveelongated segments in order to achieve area efficiency and a specificcurrent handling capability. The package also has maximum cavity size.Thus, while it is desirable to manufacture an IC on a semiconductor diehaving a substantially square shape, the need to provide a productfamily with a range of current handling capabilities which fits within apackage cavity size has constrained the dimensions of the controlcircuitry and semiconductor die 10.

The solution of the prior art has been to provide a control circuit thathas a relatively narrow width and a much larger length that issubstantially equal to the maximum package cavity size. For example, inFIG. 1 the length of control circuit 11 is about four times its width.However, this causes area inefficiencies due to control circuit wiring.Another significant shortcoming of this prior art approach is that in ICdevices with small output field-effect transistors (i.e., fewersegments) suffer from package stress problems caused by highsemiconductor die aspect ratio.

Thus, there is an unsatisfied need for an improved monolithic IC designthat overcomes the problems of poor control circuit area efficiency andhigh IC aspect ratio.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription that follows and from the accompanying drawings, whichhowever, should not be taken to limit the invention to the specificembodiments shown, but are for explanation and understanding only.

FIG. 1 shows a circuit layout of a prior art monolithic integratedcircuit.

FIG. 2 is circuit layout illustrating an integrated circuit according toone embodiment of the present invention.

FIG. 3 is a circuit schematic diagram that corresponds to the integratedcircuit shown in FIG. 2.

FIG. 4 is circuit layout illustrating an integrated circuit according toanother embodiment of the present invention.

FIG. 5 is circuit layout illustrating an integrated circuit according tostill another embodiment of the present invention.

FIG. 6 is circuit layout illustrating an integrated circuit according toyet another embodiment of the present invention.

DETAILED DESCRIPTION

An improved integrated circuit is described. In the followingdescription, numerous specific details are set forth, such as devicetypes, dimensions, circuit configurations, etc., in order to provide athorough understanding of the present invention. However, persons havingordinary skill in the semiconductor arts will appreciate that thesespecific details may not be needed to practice the present invention.

FIG. 2 illustrates a circuit layout of a monolithic IC according to oneembodiment of the present invention. (In the context of the presentapplication, the term “IC” is considered synonymous with a monolithicdevice.) In the example of FIG. 2, the IC shown may comprise a powerintegrated circuit (PIC) fabricated on a semiconductor die 20, whichincludes a first output HVFET 23 having a set of relatively shortinterdigitated source/drain segments, and a second output HVFET 24having a set of relatively long interdigitated source/drain segments.The segments of HVFETs 23 & 24 are placed on die 20 in a manner thatoptimizes the layout of control circuit 21. The arrangement of HVFETs 23& 24 also improves the layout of the complete PIC such that die 20 has abetter aspect ratio as compared to prior art devices, even forimplementations with low current handling capability. It should beunderstood, however, that the present invention is not limited to PICsand may find application in a wide variety of IC designs having amultitude of voltage and current handling characteristics.

As can be seen, output transistor 23, with the short segments, islocated on die 20 adjacent the short, lateral side of control circuit21. In one implementation, control circuit 21 comprises a switched moderegulator control circuit. Control circuit 21 and transistor 23 bothhave substantially the same width (W₁). The total length (L) ofsemiconductor die 20 is approximately equal to the sum of the lengths oftransistor 23 and control circuit 21 (L≃L₁+L₂).

In the embodiment of FIG. 2, output transistor 24 is shown located ondie 20 adjacent the long, bottom side of control circuit 21, and alsoextending beneath the length of transistor 23. The length of thesegments of output transistor 24 is substantially equal to the length(L₂) of control circuit 21 plus the length (L₁) of the segments ofoutput transistor 23. In other words, the short transistor segments areplaced alongside the short side of control circuit 11 such that thecombined control circuit and short transistor segment length issubstantially the same as the length of the long segments of transistor24. In the embodiment shown, each of the output transistors is of thesame conductivity type, i.e., n-type or p-type. (In embodiments wherethe output transistors are bipolar devices, each of the outputtransistors are also of the same type, i.e., npn or pnp devices.)

The total width (W) of semiconductor die 20 is approximately equal tothe sum of the widths of control circuit 21 and transistor 24 (W≃W₁+W₂).To manufacture an IC device with increased current handling capability,more long segments are added in parallel to transistor 24, which has theeffect of increasing the W₂ dimension and lowering the aspect ratio ofsemiconductor die 20.

Another way of viewing the embodiment of FIG. 2 is to consider theoutput transistors 23 and 24 as occupying an L-shaped area ofsemiconductor die 20, with the two inner sides of the L-shaped areabeing located adjacent two corresponding sides of control circuit 21.That is, one of the inner sides of the L-shaped area has a lengthsubstantially equal to the length (L₂) of control circuit 21, with theother inner side of the L-shaped area having a length substantiallyequal to the width (W₁) of control circuit 21. The two outer sides ofthe L-shaped area have dimensions that are substantially equal to theoverall length (L≃L₁+L₂) and width (W≃W₁+W₂) of semiconductor die 20,respectively.

Practitioners in the integrated circuit and semiconductor fabricationarts will appreciate that the embodiment shown in FIG. 2 permits controlcircuit 21 to have a layout with an optimum aspect ratio that providesbetter area efficiency than prior art designs. In the implementationshown in FIG. 2, the length (L₂) of control circuit 21 is about threetimes its width (W₁). Furthermore, the novel use and placement ofmultiple output transistors having different segment lengths results inan aspect ratio closer to 1.0 for the complete IC. This means that afamily of IC devices, each with different current handling capability,may be manufactured on a semiconductor die 20, each having an aspectratio closer to 1.0. For the embodiment shown in FIG. 2, the aspectratio of die 20 is about 1.6.

With continuing reference to FIG. 2, an IC device having a relativelysmall current handling capability may be realized by connecting controlcircuit 21 to output transistor 23, but not to output transistor 24. AnIC device having increased current handling capability may beimplemented by connecting control circuit 21 to both output transistor23 and output transistor 24, or just to output transistor 24 and notoutput transistor 23. In one embodiment, both of the output transistorsare connected in parallel to act as a single larger output transistorwhich is connected to the control circuit. In one embodiment, both ofoutput transistors 23 and 24 have a breakdown voltage greater than 100V.IC devices that provide even larger current handing capability may berealized by increasing the number of long segment of output transistor24 during the layout and manufacturing of semiconductor die 20. In eachcase, the dimensions of control circuit 21 remain the same. Reasonableaspect ratios may be maintained by extension of the length of thetransistor segments of output transistors 23 & 24 as the number ofsegments of output transistor 24 increases. In accordance with thepresent invention, a complete family of IC devices having a wide rangeof current handling capabilities may be implemented on a semiconductordie having an aspect ratio within a range of 0.5 to 2.0.

Another possible configuration is to have only one of the outputtransistors 23 & 24 coupled to control circuit 21, with the other outputtransistor being available for use as an independent transistor forconnection to other off-chip circuitry.

It should be understood that even though the embodiment of FIG. 2illustrates two output transistors with different length segments, thereis no restriction on the number of output transistors that may beincluded on die 20. That is, more than two output transistors havingdifferent length segments may be included on die 20.

For example, an IC with four output transistors may be implemented inwhich two additional transistors are located side-by-side on die 20above or below transistor 24. The two additional output transistors mayhave a combined segment length that is approximately equal to the sum ofthe lengths of transistor 23 and control circuit 21 (L≃L₁+L₂). In suchas case, the segment lengths of the two additional transistors may havean intermediate length that is longer than that of the short segments oftransistor 23, yet shorter than the length of the long segments oftransistor 24. These additional transistors with intermediate lengthsegments may be selectively coupled to control circuit 21 to implementan IC device providing an intermediate range of output current capacity.

Persons of ordinary skill in the integrated circuit and semiconductorarts will appreciate that selective coupling between control circuit 21and one or both of the output transistors 23 & 24 may be achievedutilizing a variety of conventional techniques and circuits. Forexample, an optional metal connection may be implemented during thelayout and fabrication of the IC. Alternatively, an ordinary on-chipswitching circuit may be utilized for selectively coupling one or moreof the output transistors to control circuit 21. This switching circuitmay be incorporated into the layout of control circuit 21 and maycomprise one or more transistor switching devices (e.g., transmissiongates).

FIG. 3 is a circuit schematic diagram that corresponds to the monolithicpower integrated circuit shown in FIG. 2. As explained previously,control circuit 21 may be selectively coupled to output transistor 23 orto output transistor 24, or to both transistors 23 & 24. This lattercase is depicted by the dashed line showing a common connection to eachof the three terminals (i.e., source, drain, and gate) of the respectiveoutput transistors. In one embodiment the output transistors are HVFETsthat are connected in parallel to effectively act as a single HVFETwhich is switched on and off by the control circuit. In one embodimentthe control circuit is a switching regulator circuit. Alternatively, theoutput transistors may have only one or two terminals coupled together(i.e., only the source terminals).

With reference now to FIG. 4, an alternative embodiment of an integratedcircuit according to the present invention is shown including a controlcircuit 25 that occupies an L-shaped corner area of semiconductor die20. In this embodiment, one outer side of the L-shaped area occupied bycontrol circuit 25 has a length L₂, with the other outer side having adimension substantially equal to the overall width (W≃W₁+W₂) ofsemiconductor die 20. Output transistors 23 and 24 occupy an L-shapedarea of die 20 adjacent to control circuit 25, such that die 20 has anoverall rectangular shape with an aspect ratio within a range of 0.5 to2.0. In this example, output transistor 23 is located adjacent theleft-hand side of control circuit 25 and has a width W₁ that issubstantially equal to the width of the upper portion of control circuit25. Either one (or both) of the output transistors 23 & 24 is coupled tocontrol circuit 25. In FIG. 4 output transistor 24 is shown locatedbeneath output transistor 23 and adjacent the upper inner side ofcontrol circuit 24. In this embodiment, the length of the transistorsegments of output transistor 24 is less than the overall length ofsemiconductor die 20, which overall length (L) is substantially equal tothe sum of the length (L₁) of output transistor 23 plus the length (L₂)of the upper section of control circuit 25.

FIG. 5 shows yet another alternative embodiment of the present inventionthat includes a standardized control circuit 21 coupled to one or bothof output transistors 27 and 28. In this embodiment, output transistor28 occupies an area adjacent one side of control circuit 21 and hastransistor segments substantially equal to a length L₁. Unlike theembodiment of FIG. 2, however, output transistor 28 has a much greaternumber of segments such that the width of transistor 28 is substantiallyequal to the overall width (W) of semiconductor die 20. Outputtransistor 27 has a plurality of transistor segments, each of which hasa length substantially equal to the length (L₂) of control circuit 21.The width (W₂) of output transistor 27 plus the width (W₁) of controlcircuit 21 is substantially equal to the overall width (W) ofsemiconductor die 20. Like the previous embodiments, control circuit 21is selectively coupled to one or both of output transistors 27 & 28.

FIG. 6 illustrates an integrated circuit in accordance with stillanother alternative embodiment of the present invention. The embodimentof FIG. 6 includes an output transistor 27 disposed adjacent one side ofcontrol circuit 21, as in the embodiment of FIG. 5. The single outputtransistor 28 of FIG. 5, however, is replaced in FIG. 6 by a pair ofoutput transistors 23 & 29 that occupy the same area adjacent theleft-hand sides of transistor 27 and control circuit 21. Bothtransistors 23 & 29 have segments with substantially the same length(L₁). Output transistor 23 has a width substantially equal to the width(W₁) of control circuit 21. Output transistor 29 has a widthsubstantially equal to the width (W₂) of output transistor 27. In theembodiment of FIG. 6, control circuit 21 is coupled to one or more oftransistors 23, 27, and 29, depending on the current handling capacityrequired. For example, in applications requiring maximum currenthandling capacity control circuit 21 would be coupled to all threetransistors 23, 27, and 29. In cases where less than all of the outputtransistors are connected to control circuit 21, the unconnected outputtransistors may be available for use as independent transistor s coupledto other off-chip circuitry.

Although the present invention has been described in conjunction withspecific embodiments, those of ordinary skill in the arts willappreciate that numerous modifications and alterations are well withinthe scope of the present invention. Accordingly, the specification anddrawings are to be regarded in an illustrative rather than a restrictivesense.

1. A method of manufacturing an integrated circuit (IC) on asemiconductor die, the method comprising: locating a control circuit ina first area of the semiconductor die, the control circuit having alength that extends along a first side and a width that extends along asecond side; locating a first output field-effect transistors (FETs)adjacent the second side of the control circuit, the first output FEThaving a width substantially equal to the width of the control circuit;locating a second output FET adjacent the first side of the controlcircuit, the second output FET having a length substantially equal tothe length of the control circuit plus a length of the first output FET,the length of the second output FET being at least 20% longer than thelength of the control circuit; coupling the control circuit to at leastone of the first or second output FETs; and wherein the control circuit,first output FET, and second output FET are sized such that thesemiconductor die has an aspect ratio within a range of 0.5 to 2.0. 2.The method of claim 1 wherein the first and second output FETs eachcomprise interdigitated segments, the interdigitated segments of thesecond output FET being substantially longer than the interdigitatedsegments of the first output FET. 3-32. (canceled)
 33. A method ofmanufacture of an integrated circuit (IC), the method comprising:locating a control circuit in a first area of the semiconductor die, thecontrol circuit having a length that extends along a first side and awidth that extends along a second side; locating a first outputtransistor adjacent the second side of the control circuit, the firstoutput transistor having a width substantially equal to the width of thecontrol circuit; locating a second output transistor adjacent the firstside of the control circuit, the second output transistor having alength substantially equal to the length of the control circuit plus alength of the first output transistor; and coupling the control circuitto at least one of the first or second output transistors.
 34. Themethod of claim 33 wherein the first and second output transistors eachcomprise interdigitated segments, the interdigitated segments of thesecond output transistor being substantially longer than theinterdigitated segments of the first output transistor.
 35. The methodof claim 33 wherein the semiconductor die has an aspect ratio within arange of 0.5 to 2.0.
 36. The method of claim 33 wherein the first andsecond output transistors each have a breakdown voltage greater than100V.
 37. The method of claim 33 wherein the control circuit comprises aswitched mode regulator control circuit. 38-43. (canceled)